Safe load indicators for jib cranes



Jan. .13, 1970 B. G. NIXON SAFE LOAD INDICATORS FOR JIB CRANES 4 Sheets-Sheet 1 Filed July 5, 1967 L M abla Jan. 13, 1970 B. G. NIXON SAFE LOAD INDICATORS FOR JIB CRANES 4 Sheets-Sheet 2 Filed July 5, 1967 Jan. 13, 1970 B. 5. NIXON SAFE LOAD INDICATORS FOR JIB (IRA NBS 4 Sheets-Sheet 5 Filed July 5, 1967 Jan. 13, 1.970 B. G. NIXON SAFE LOAD INDICATORS FOR JIB CRANES Filed July 5, 1967 United States Patent 3,490,015 SAFE LOAD INDICATORS FOR JIB CRANES Brian George Nixon, Kew Gardens, England, assignor to Weighload Limited, London, England, a British company Filed July 5, 1967, Ser. No. 651,304 Claims priority, application Great Britain, July 7, 1966, 30,626/ 66 Int. Cl. G08b 21/00 U.S. Cl. 340-267 Claims ABSTRACT OF THE DISCLOSURE A safe load indicator for a crane having a telescopic jib which includes means for adjusting, in accordance with variation in the length of the jib, a pointer indicating the safe load at a particular working radius of the crane.

In United States Patent'No. 3,278,925 is described and claimed an overload warning device for a luffing crane comprising a device for measuring the load suspended by the jib of the crane, a first indicating member controlled by the load measuring device and arranged to move progressively from one end of an indicating path in response to increase in the load, a slave jib adapted to move angularly with the jib of the crane to positions representative of the working radius of the crane, a transmission member actuable by the slave jib and arranged to execute a linear movement which is proportional to the angular movement of the slave jib, means for coupling the transmission member to the slave jib at difierent points along the length of the slave jib corresponding to crane jibs of different length, a second indicating member controlled by the transmission member and arranged to move progressively from the other end of the indicating path in response to increase in the working radius to positions in the path indicative of the safe load at any particular working radius, and means operable by approach of the two indicating members to issue a warning signal when an overload condition is approached.

The present invention is concerned with an improved form of overload warning device suitable for use with a crane having a telescopic jib including a movable upper extension. It provides an overload warning device as described in United States Patent No. 3,278,925 for use with such a crane which comprises means movable in response to movement of the extension of the jib for effecting automatically adjustment of the coupling means between the slave jib and the transmission member to compensate for change in the length of the jib. Such adjustment is necessary because the safe working radius at any particular load will depend upon the length of the jib.

Preferably the device comprises a lead screw mounted in the slave jib and a cooperating nut constrained to move along the slave jib without rotation in response to rotation of the lead screw, a pin on the nut which engages a slot in the transmission member and means for rotating the lead screw in a direction and to an extent determined by the direction and extent of the movement of the extension of the jib. The means for rotating the lead screw may comprise a spring loaded drum carrying a cable for connection to the extension of the jib and a flexible shaft for imparting rotation to the lead screw from the drum.

Since the linear movement of the transmission member is directly proportional to the working radius of the crane, it may carry a pointer which coacts with a scale to provide a radius indicator. Alternatively, the pin may carry a pointer which coacts with two scales which respectively provide indications of the working radius and of the length of the jib of the crane.

Two embodiments of the invention will now be further explained, by way of example, with reference to the accompanying drawings in which:

FIG. 1 is a side elevation of mobile lufiing crane,

FIG. 2 is a vertical section, on a larger scale, through a. control box housed within the cabin of the crane,

FIG. 3 is a front elevation of the lower part of the control box showing it equipped with a radius indicator,

FIG. 4 is a similar view showing the control box fitted with an indicator which shows both working radius and jib length, and

FIGS. 5 and 6 are diagrams showing respectively the visual and audible warning systems.

The crane shown in FIG. 1 includes a telescopic jib consisting of a lower section 11 pivoted at 12 to a wheeled carriage 13 and a top extension 14 which can be moved upwardly or downwardly with respect to the lower section 11 in conventional fashion by a hydraulic cylinder 15 operable by the crane operator who occupies a cabin 16. The overload indicator is housed within a control box 17 in the cabin.

As in the case of the indicator described in United States Patent No. 3,278,925, the indicator includes two pointers 18, 19 (FIG. 2) which move in opposite directions over a scale 20 calibrated in terms of the actual load suspended from the rope 21 (FIG. 1) of the crane. The rope 21 extends from a winding drum 22 over pulleys 23, 23A at the top of the jib and carries a hook for supporting the load. The load on the rope 21 is measured by a dynamometer 25, mounted on the jib and of the construction described in United States Patent No. 3,310,981.

As described in United States Patent No. 3,278,925, the dynamometer includes a hydrostatic load cell which is connected to a pressure gauge for actuating the pointer 18, so that the pointer 18 will move clockwise over the scale 20, as seen in FIG. 2, in response to increase in the load on the rope 21. The pointer 19 is moved counter clockwise over the scale 20 in response to increase in the working radius of the crane as described below. The indicator includes electrical controls, operated as described in United States Patent No. 3,278,925 to light a warning lamp upon approach of the pointers 18, 19 and to ring a bell upon further approach of the pointers.

These controls are shown in FIGS. 5 and 6. Two controls are attached to and move with the pointer 18, one contact 64 (FIG. 5) serving to give a visual overload warning and the other contact 65 (FIG. 6) serving to give an audible overload warning. A slip ring 66 (FIG. 5) moves in unison with the pointer 19 and when the pointers 18, 19 come into coincidence the contact 64 meets a contact 67 on the slip ring and completes a circuit to light a warning lamp 68. Another electrical contact 69, which is offset angularly from the pointer 19 by an angle a: (FIG. 6) which represents a constant proportion of the safe working load, is rotated by the pointer 19 through a secondary gear train, comprising gear wheels 70 and 71. If the working radius is increased after the visual warning has been given, the pointers 18, 19 will pass each other and, after the working radius has increased to an extent representing said constant percentage of safe working load, the contacts 65 and 69 will meet, completing a circuit through a slip ring 72 to ring a bell 73. The warning lamp 68 remains onuntil the bell 73 has begun to ring, both signals thereafter continuing.

A slave jib 26 (FIG. 2) is pivotally mounted at its lower end in the control box 17 and carries a pulley 27 which is connected to a pulley 28 on the jib by a flexible drive constituted by Bowden cables 29. The slave jib 26 accordingly moves with the jib and maintains the same inclination to the vertical as the jib. A lead screw 30 is rotatably mounted in the slave jib 26 and carries a nut 31 which is threaded onto the lead screw 30 and has a boss (not shown) which engages a slot 32 in the slave jib 26 so that the nut is constrained against rotation but is nevertheless free to travel axially along the lead screw 30 as the latter is rotated. The nut 31 carries a pin 31A, fixed to the nut, on which is rotatably mounted a block 33 having a portion which engages a longitudinal slot 34 in a transmission member 35 which is mounted to travel laterally in the control box on bars 36. A cam follower 37 on the transmission member 35 engages a cam slot 137 in an arm .38, which is pivoted at 39 and carries a toothed qua-drant 40, which meshes with a gear 41 which transmits rotary movement from the quadrant to a gear 42 attached to the pointer 19.

Rotation of the slave jib 26 will therefore cause the block 33 to impart lateral movement to the transmission member 35 to rock the quadrant 40 and rotate the pointer 19. The lead screw 30 is coupled to the extension 14 of the jib as described below so that it is rotated in a direction and to an'extent corresponding to the direction and extent of the movement imparted to the extension 14 by the cylinder 15. The position of the nut 31 in the slot 32 is thus determined by the length of the jib and movement of the nut 31 in the slot 32 upon rotation of the lead screw 30 will also cause the block 33 to move the transmission member 35 laterally to adjust the pointer 19. The cam slot 137 is so formed that the position of the pointer 19 indicates on the scale the safe load at each working radius of the crane.

The extension 14 of the jib (FIG. 1) is connected by a cable 43 to a spring drum 44 which is accordingly rotated by upward or downward movement of the extension and is connected by a flexible drive shaft 45 and bevel gears 46 (FIG. 2) to the lead screw which is thus rotated in accordance with the movements imparted to the extension 14.

As shown in FIG. 3, a pointer 47 may be attached to a. projection 48 (FIG. 2) on the transmission member and coact with a scale 49 visible through a window 50 in the control box and calibrated to show the working radius of the crane. Alternatively, as shown in FIG. 4, a pointer 51 may be fitted to the pin 31A and coact with a scale marked with lines 52 indicating working radius and with other lines 53 indicating jib length.

What I claim as my invention and desire to secure by Letters Patent is:

1. An overload warning device for a luffing crane having a telescopic jib which includes a movable upper extension, said device comprising a device for measuring the load suspended by the jib of the crane, a first indicating member controlled by the load measuring device and arranged to move progressively from one end of an indicating path in response to increase in the load, a slave jib adapted to move angularly with the jib of the crane to positions representative of the working radius of the crane, a transmission member actuable by the slave jib and arranged to execute a linear movement which is proportional to the angular movement of the slave jib, means for pivotally coupling the transmission member to the slave jib at different points along the length of the slave jib corresponding to crane jibs of different length, a second indicating member controlled by the transmission member and arranged to move progressively from the other end of the indicating path in response to increase in the working radius to positions in the path indicative of the safe load at any particular working radius, means movable in response to movement of said extension of the jib for automatically shifting said coupling means along the length of the slave jib to compensate for change in the length of the jib, and means operable by approach of the two indicating members to issue a Warning signal when an overload condition is approached.

2. A device as claimed in claim 1, wherein said means automatically shifting said coupling means comprises a lead screw mounted in the slave jib and wherein said pivotal coupling means consists of a nut threaded to the lead screw constrained to move along the slave jib without rotation in response to rotation of the lead screw, a pin on the nut and means on the pin which engages a slot in the transmission member, and means for rotating the lead screw in a direction and to an extent determined by the direction and extent of the movement of the extension of the jib.

3. A device as claimed in claim 2, in which the means for rotating the lead screw comprises a spring loaded drum carrying a cable for connection to the extension of the jib and a flexible shaft for imparting rotation to the lead screw from the drum.

4. A device as claimed in claim 2, in which the transmission member carries a pointer which coacts with a scale to provide a radius indicator.

5. A device as claimed in claim 2, in which the pin carries a pointer which coacts with two scales which respectively provide. indications of the working radius and of the length of the jib of the crane.

References Cited UNITED STATES PATENTS 2,988,040 6/1961 Aitken. 3,123,814 3/1964 Aitken. 3,148,659 9/1964 Aitken. 3,278,925 10/1966 Saundors et al.

LOUIS R. PRINCE, Primary Examiner D. M. YASICH, Assistant Examiner I U.S. Cl. X.R. l16-124 

